1. Field of the Invention
The present invention relates to a dual-intake fan which is a so-called sirocco fan used for venting air, and more particularly, to a fan having a structure in which a portion of an exhaust outlet is formed to be inclined while the centers of a scroll housing and an impeller are disposed to be eccentric so that noise can be reduced while air flow can be effectively guided by the scroll housing to the maximum extent and the air flow rate can be increased.
2. Description of the Related Art
In general, a fan, as a device which generates air flow, is widely used in various equipments and facilities. In particular, in a microwave oven provided with a fume hood, which is used in a domestic kitchen, a fan is installed at an upper portion of the microwave oven so as to vent odors and smoke generated in a gas range installed below the microwave oven. That is, as shown in FIGS. 1 and 2, after the odors and smoke generated in the gas range are drawn into the lower part of the microwave oven, the odor and smoke are taken into a fan 10 along air flow passages, and then are vented to the outside through an exhaust outlet 10a of the fan 10. Here, the exhaust outlet 10a of the fan 10 may be installed as shown FIG. 2, or may be configured so that the exhaust outlet 10a is installed to face upward and the odors and smoke can be vented to the outside by connecting a duct to the exhaust outlet 10a. As a matter of course, in the microwave provided with the fume hood, a magnetron 2 for generating an electromagnetic wave so as to cook food supplied into a cooking chamber 1a, and a fan 3 for cooling the magnetron 2. Reference numerals 1, 4, and 11 indicate a case, a door and a motor, respectively.
FIG. 3 shows a front view of a conventional fan, FIG. 4 shows a left side view of the fan shown in FIG. 3, FIG. 5 shows a left side view of the fan shown in FIG. 3 illustrating a flow velocity distribution measured by a laser Doppler velocimeter (LDV) at the exhaust outlets of the fan, and FIG. 6 shows a front view of the fan shown in FIG. 3, in which a flow velocity distribution at an air inlet of the fan is expressed by velocity vectors.
As shown in FIGS. 3 and 4, a conventional fan 20 comprises impellers 21 for rotating so as to create air flow, scroll housings 22 for guiding the flow of air drawn by the impeller 21, bell mouths installed around air inlets 22a formed at the scroll housings 22 for guiding intake air flow.
Here, the impeller 21 comprises a plurality of blades 21a for rotating so as to create air flow, rims 21b installed at both ends of the blades 21a for supporting the blades, and a separating member 21c connected to a motor 30 as a driving means while connected to center portions of the blades.
In addition, the air inlets 22a are formed at the motor side and the flow passage side of the scroll housing 22, and an exhaust outlet 22b for venting the air drawn into the scroll housing 22 through the air inlets 22 is formed at the scroll housing 22. Here, the reference location or boundary location of the exhaust outlet 22b is called a cutoff C'.
In the above structure, when the motor 30 is supplied with electric power and the impeller 21 rotates, air is drawn in through the air inlet 22b by the pressure due to the rotation of the impeller 21. After the drawn air is moved to the exhaust outlet 22b in accordance with the guidance of the scroll housing 22 having a gradually expanding passage from the cutoff C', the air is vented to the outside. That is, the entering air to which the dynamic energy is imparted by the blades 21a, the air is vented to the outside through the exhaust outlet 22b while recovering static energy from the dynamic energy.
Reference numerals S' and I' indicate the center of the air inlet 22a of the scroll housing 22a and the rotation center of the impeller 21, respectively.
However, in the conventional fan 20, since the exhaust outlet 22b of the scroll housing 22 has a rectangular shape parallel to the rotating shaft of the impeller 21, it was found that relatively large flow loss occurs at the edge portions, i.e., the peripheral portions of the exhaust outlet 22b as shown in FIG. 5, as a result of an experiment of measuring a flow velocity distribution at the exhaust outlet 22b with the laser Doppler velocimeter. In other words, the air flow having a recovered pressure, i.e., raised static energy while flowing along the scroll housing 22 forms a wide flow loss area due to the growth of boundary layers at the edge portions of the exhaust outlet 22b. Accordingly, there are problems in which while such flow loss at the exhaust outlet reduces the air flow rate, the lost energy is converted into noise and increases noise.
In addition, since the conventional fan 20 is designed so that the center I' of the impeller is simply coincident with the center S' without considering the flow velocity distribution at the air inlet 22a, as shown in FIG. 6 when examining the flow velocity distribution at the air inlet 22a of the fan, there is a problem in which a flow loss area L is formed in an area where the rotation angle .theta.' is in the range from -90.degree. to 90.degree. when examined in terms of the rotation angle .theta.'.